Persist database regardless of notebook or script

[bkamapantula]

persist() is required even if it's invoked in a script apart from in a notebook.

Without this, an error is thrown

chromadb.errors.NoIndexException: Index is not initialized

[sifatulrabbi]

When I ran this as a script it persisted the information without calling the vectordb.persis().

python 3.11.5
langchain==0.0.310
chromadb==0.4.13